Deionizers with energy recovery

ABSTRACT

Deionizers using the electrode configurations of electrochemical capacitors are described, wherein the deionizing process is called capacitive deionization (CDI). During deionization, a DC electric field is applied to the cells and ions are adsorbed on the electrodes with a potential being developed across the electrodes. As electrosorption reaches a maximum or the cell voltage is built up to the applied voltage, the CDI electrodes are regenerated quickly and quantitatively by energy discharge to storage devices such as supercapacitors. In conjunction with a carousel or Ferris wheel design, the CDI electrodes can simultaneously and continuously undergo deionization and regeneration. By the responsive regeneration, the CDI electrodes can perform direct purification on solutions with salt content higher than seawater. More importantly, electrodes are restored, energy is recovered and contaminants are retained at regeneration, while regeneration requires no chemicals and produces no pollution.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of, and claims the prioritybenefit of, U.S. application Ser. No. 10/109,825 filed on Mar. 27, 2002U.S. Pat. No. 6,580,598.

References Cited 4,765,874 August 1988 Modes et al. 4,991,804 March 1991Pekala 5,779,891 July 1998 Andelman 5,858,199 January 1999 Hanak5,954,937 September 1999 Farmer et al. 6,051,096 April 2000 Nagle et al.6,168,882 January 2001 Inoue et al. 6,267,045 July 2001 Wiedemann et al.6,309,532 October 2001 Tran et al. 6,326,763 December 2001 King et al.6,328,875 December 2001 Zappi et al.

OTHER REFERENCES

J. Newman et al, J. Electrochem. Soc., 128, PP510-517(1971), “Desaltingby Means of Porous Carbon Electrodes”

I. Parikhi; P. Cuatrecasas, C&EN, Aug., 26, 1985, PP17-32(1985),“Affinity Chromatography”

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention relates generally to capacitive deionization (CDI) ofliquids containing charged species, including aqueous, inorganic andorganic solutions. More particularly, this invention relates torecurrent electrosorption of ions (deionization) and regeneration ofelectrodes whereby energy is extracted and stored in supercapacitors,ultracapacitors, or electric double layer capacitors. The presentinvention provides deionizors wherein purified liquids and electricityare co-generated.

2. Description of Related Art

Energy and water are two essential ingredients of modern life. Since thefossil fuel is diminishing and generates pollution at power generation,people become more eager in searching for alternative sources of energy.Therefore, renewable energy sources such as solar power, wind power,wave power, and geothermal heat have been explored and commercialized.Many international automakers are aggressively developing fuel cells forpollution-free electric vehicles. All of the above endeavors are aimedto reduce CO₂ emission and to use natural free resources such as sun andwater for energy production. Production of energy is no easy matter,hence conservation of energy that includes controlled usage andresponsive extraction of energy deserves attention. There are numerousviable ways for retrieving residual energy that would be otherwisewasted. For example, U.S. Pat. No. 6,326,763 issued to King et aldisclosed a regenerative braking system that can store electricityconverted from the remaining momentum of vehicle during periods ofdeceleration due to braking for stop or moving down hill.Ultracapacitors were proposed in '763 to extract the residual energythat is generally dissipated as heat. In another example, U.S. Pat. No.6,267,045 issued to Wiedemann et al revealed a cooking device containingan energy storage and energy extraction system wherein energy isexchanged in the form of latent heat.

Less than 1% of water on the earth surface is suitable for direct use.Fresh water will be one of the precious commodities in the 21st century.In lieu of rainfall, desalination of seawater is probably the mostplausible means to attain fresh water. Among the commercial desalinationmethods, distillation dominates the market with 56% share, reverseosmosis (RO) possesses 40%, while freezing and electrodialysis seize therest. The aforementioned methods though are different in thepurification mechanisms, they are all utilized to reduce the totaldissolved solids (TDS) which is a measure of charged species insolutions so that seawater can become potable. Reduction of TDS, ordeionization, is also an ultimate goal for waste liquid treatments whereion exchange and RO are most frequently used. In purifying seawater orwaste liquids, the employed method should be a low energy-consumption,pollution-free, and long service-life technique. In fulfilling theforegoing requirements, capacitive deionization (CDI) is a superiormethod than ion exchange, RO, and other techniques for deionization.There are five reasons to vindicate the supreme merit of CDI: (1) CDIuses a DC electric field for adsorbing and removing ions from solutions,the process is quick and controllable with minimal energy consumption.(2) Energy that is input for electrosorption can be extracted and storedfor latter use or other applications. No energy recovery is available inany of the aforementioned separation methods. (3) While energy istransferred from the CDI electrodes to a load, the electrodes arerestored simultaneously. Regeneration of CDI electrodes by energyextraction is prompt without using chemicals and without producingpollution. (4) CDI can directly deionize seawater or solutions with TDShigher than 35,000 ppm. Deionization and regeneration can be repeatednumerous times until the liquids are clean, and the electrodes are notdegraded by the high salt content. Whereas RO, electrodialysis, and ionexchange are better utilized for treating low salt-content solutions.Otherwise, their expensive membranes or resins will be damaged quickly.(5) Ions that are adsorbed by the CDI electrodes can be discharged in aconcentration reservoir for recycling useful resources or for sludgedisposal. Extraction of ions by CDI is a non-destructive process, thussome ions may be processed for reuse. The invention will demonstrate allof the foregoing five unique features of the CDI technique in the lattersection of detailed description. Incidentally, energy recovery in thedeionizers is consistent with the ultimate principle of free energytapping, that is, no fuel should be added and no pollutant should beemitted.

CDI is a separation methodology that is known for more than 40 years (J.Newman et al, 1971). Just to name a few, U.S. Pat. Nos. 5,799,891,5,858,199, 5,954,937 and 6,309,532 are all intended to commercialize theCDI technique. Particularly, '532 issued to Tran et al disclosed the useof electrical discharge for regenerating electrodes. Rather thanreclaiming the residual energy, the electricity is dissipated byshorting or reverse polarity (claims 4, 18, 21, and 23). Shorting afully charged capacitor may cause electrical hazards particularly whenthe energy accumulated is immense. It is known to people skilled in theart that reverse polarity would momentarily expel the adsorbed ions fromthe electrodes. However, the ions would leave one electrode and then beadsorbed by the other electrode, unless an alternate polarity reversalof appropriate frequency is applied in conjunction with a large quantityof fluid for flushing the desorbed ions out of the cell. This mayexplain why 40 liters of liquid was used for every cycle of regenerationin Example 1 of '532. In addition, one cycle regeneration of the CDIelectrodes of '532 takes several hours to accomplish, such lengthyprocess is unprofitable for commercial application. As indicated by FIG.12 of '532, deionization as proposed was equally slow as a reduction ofTDS by 59 ppm (100 μS divided by conversion factor 1.7) using 150 pairsof 10×20 cm² electrodes, or a total geometric area of 30,000 cm², took10 minutes of processing time. Moreover, '532 taught a serpentine liquidflow pattern in a complex cell as shown by FIG. 3 wherein 150 pairs orother combination of electrodes were stacked and compressed. Forcreating the liquid path, apertures were specifically fabricated on theelectrode supports whereon carbon aerogel, lithographically perforatedmetal, or costly metal carbides were used as the electrosorptive medium.Usage of the foregoing designs and materials will add cost to the CDIcells and present difficulties to operation, as well as maintenance. Incomparison, disclosures of the present invention will furnishcost-effective, high-throughput, and user-friendly deionizers forpurifying contaminated liquids and for desalinating seawater. Afterpartial or complete adsorption of ions, the deionizers can be dischargedat different rates to deliver constant currents or peak currents todifferent loads as required. In other words, the deionizers can beutilized as liquid purifiers, as energy-storage devices, and as powerconverters.

SUMMARY OF THE INVENTION

Practically, CDI has adopted the charging mechanism of supercapacitor(other nomenclatures for the device include ultracapacitor and electricdouble layer capacitor) for removing ions from solutions in thisinvention. Supercapacitor is an electrochemical capacitor that can storestatic charges up to several thousands of farad (F), and it can becharged and discharged quickly. As the electrodes of supercapacitoraccumulate ions on their surface, a DC potential is developed withincreasing charges across the positive and negative electrodes of thecapacitor. Such voltage rise with ion accumulation relationship is alsoobserved during deionization by CDI process. Therefore, voltage can beused to determine if the CDI electrodes have reached an adsorptionmaximum, or they have reached an equilibrium state where the inducedpotential is equal to the applied voltage. In either case, the CDIelectrodes require regeneration for further service. Following thegeneral electrode configurations of supercapacitors, that is, stackingor winding, the CDI electrodes are similarly constructed and assembledinto modules but with two variations. Firstly, unlike the separatorsreserve electrolytes for the supercapacitors, components other than theelectrosorptive medium in the CDI modules should neither adsorb norretain ions. Secondly, unlike the electrodes of supercapacitors areenclosed in protecting housings, the CDI electrodes are merely securedby simple means such as tape without encapsulation. Hence, the CDIelectrodes of the present invention are widely open to the surroundings,and fluids to be treated have free access to the electrodes. With theforegoing flow-through design, the CDI modules can be placed in fluidconduits for deionization, or they can be submerged in liquids andcruised like a submarine to remove ions.

Not only the electrodes are assembled using the minimal amount ofsupporting materials, readily available activated carbon of low price isalso used as the electrosorptive medium for further reducing the cost ofCDI modules. Carbon material is deposited onto an electricallyconductive substrate by an inexpensive process such as roller coating toform the CDI electrodes. With cost-effective materials, easy fabricationof electrodes, and simple assembly of electrodes, the deionizers canbecome reliable consumer products affordable to families and industries.

Just like the stored energy of supercapacitors can be quickly extractedvia discharge, the residual energy of the CDI electrodes afterelectrosorption of ions is also available for fast tapping. Though theenergy that is reclaimed is far less than the energy that is input fordeionization, the residual energy is free and addible for practicalapplications. Besides, same as the supercapacitors having 100% dischargedepth, the energy stored on the CDI electrodes can be completely drainedas well, and the electrodes are thoroughly cleaned as a consequence ofenergy recovery. To store the residual energy reclaimed from the CDImodules, supercapacitors, or ultracapacitors, or electric double layercapacitors are particularly well suited as the storage devices. This isdue to the devices are more efficient in storing energy than otherdevices such as batteries and flywheels. As long as the source voltageis higher than the voltage of supercapacitors, the capacitors can alwaysbe charged regardless of the magnitude of charging current. When the CDImodules are installed on a carousel or Ferris wheel, the electrodes canthen be reciprocally and continuously engaged in deionization andregeneration. Because of swiftly recurrent deionization andregeneration, the deionizers have high throughputs for purifyingcontaminated liquids as well as for desalinating seawater. It isexperimentally observed that the repeated deionization and regenerationcause no damage to the deionizers.

Restoration of the CDI electrodes by energy extraction is operational inany liquids including seawater. Only the adsorbed ions are discharged toa liquid, thus the liquid has no influence on regeneration and there isno second pollution. Furthermore, no flushing liquid or regenerant fluidis required to discharge the ions for they are automatically dissipatedat energy recovery. Except a minimal amount of clean liquid may beneeded to rinse the electrodes, the regeneration produces no wasteliquid. Ions are adsorbed by the CDI electrodes under a DC electricfield whereby the applied voltage can be controlled below thedecomposition potentials of ions. Thence, the CDI electrodes may beutilized as a magnet to non-destructively take ions out of liquids andto place them in a concentrating container. Once the ions areconcentrated in a small volume of liquid, useful resources can be easilyrecycled or the sludge can be effectively disposed. It is during theperiod when the restored electrodes are returned from the concentratingcontainer to the deionization chamber that rinsing may be required.

Deionization of solutions by CDI only requires the application of low DCvoltages, thus it is operable by batteries, fuel cells, and solar cells.Most of the latter devices have poor power densities. Nevertheless,after the residual energy is stored in supercapacitors, the capacitorscan then deliver peak powers to various heavy loads. From this aspect,the deionizers behave as power converters using adsorption anddesorption for energy transference. Because of various electricalresistances and other forms of energy loss such as electrolysis, thecycle of adsorption and desorption, or charge and discharge is not aperpetual motion. Nevertheless, using the deionizer of this invention asa power converter may provide some practical applications.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary, and are intended toprovide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention. In the drawings,

FIG. 1A is the first top view of two CDI electrode modules installed ina two-compartment carousel. One compartment is designated fordeionization, and the other for regeneration. As the carousel rotates,the regenerated electrode module will perform deionization while thesaturated module will undergo regeneration.

FIG. 1B is the second top view of the two-compartment carousel. It showsone electrode module can receive electricity from power supply B fordeionization, and the other module can release its residual energy toload C.

FIG. 2A is a side view of two CDI electrode modules installed in aFerris wheel. The wheel has both lifting and rotating mechanisms thatcan switch the modules from deionization to regeneration, or fromregeneration to deionization as required. Using the Ferris wheel design,only a few sets of CDI modules are sufficient for purifying contaminatedliquids and for desalinating seawater.

FIG. 2B is a top view of a Ferris wheel containing 8 compartments and 8CDI modules. The compartments are divided into three zones fordeionization, regeneration, and post-treatment.

FIG. 3 is a side view of another type of Ferris wheel where a conveyorcarrying cylindrical CDI modules. There are three sections fordeionization, regeneration, and post-treatment.

FIG. 4 is a control module that is composed of a step-up circuitry, amicroprocessor and a supercapacitor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

There are two major functions by which activated carbon removescontaminants from liquids, and they are surface adsorption and catalyticreduction. Adsorption generally occurs via some kind of affinity betweenthe contaminants and the adsorbing surface. Since the adsorptive forcesare weak and the adsorption is subject to a slow thermodynamic control,activated carbon has to rely on its large surface area and theinfinitesimal proximity between its surface and the contaminants formassive purification. However, under the application of a DC electricfield, adsorption on activated carbon can be expedited. Also, due to thepolarity built on the surface of activated carbon, the carbon willadsorb ions of opposite polarity and a selective adsorption is created.With large surface area, the charged carbon can quickly adsorb a largenumber of ions. Even without the application of an electrical field, theadsorbed ions can still remain on the surface of activated carbon for aperiod of time. The foregoing features make activated carbon attractiveas an electrosorptive material for liquid purification. Large surfacearea is the primary reason that activated carbon is commonly used forfabricating energy-storage devices such as supercapacitors, as well asfor deionization and desalination. Other considerations that activatedcarbon is preferred include inert nature, wide availability, maturetechnology, and low price. In addition, when carbon nanotube (CNT) isavailable in large quantity of suitable cost, CNT would be another idealcandidate as the electrosorptive material for the CDI electrodes.

FIG. 1A shows a preferred embodiment of the invention wherein twoelectrode modules consisting of 7 pairs of electrodes each are placed ina two-compartment carousel 10. The compartment 12 contains a liquid 20to be treated and a first electrode module having electrodes connectedin parallel to form an anode 16 and a cathode 18, respectively. By usingelectrical cables, the anode 16 and the cathode 18 are connected to thecorresponding positive and negative poles of a DC power source B,electricity is then supplied to the module for deionizing the liquid 20.Similarly, the compartment 14 contains a liquid 24 as a regenerationmedium and a second electrode module, which had been used fordeionization, for discharging its residual energy to load C through ananode 16′ and a cathode 18′. The liquid 24 can be a clean solvent or thesame liquid as 20 to provide a medium for the adsorbed ions to bedischarged. The medium will have no influence on ion discharge or energyextraction. The carousel 10 has a motor (not shown) built at the bottomof a central pole 22 for rotating the electrode modules in the directionindicated by A. As soon as one module is saturated and the other isfully restored, they will be switched positions for a new cycle ofelectrosorption and regeneration. Before rotating the carousel, theliquids 20 and 24 are drained (liquid conduits and control valves arenot shown) so that new liquids of 20 and 24 can be refilled into thecompartments 12 and 14 for deionization and regeneration, respectively.If the liquid 20 has a low salt content and can be purified in one cycleof deionization, the purified liquid is retreated for use or fordisposal to sewer. Whereas the liquid 24 can be recycled indefinitely tocollect ions released during regeneration.

Another preferred embodiment of provision for the recurrent deionizationand regeneration, or sorption and desorption, is by lifting theelectrode modules up and switching their positions for deionization andregeneration. In this operation, both chambers 12 and 14 as well asliquids 20 and 24 are stationary so that the liquid 20 can becontinuously deionized until it is acceptable for release, while theliquid 24 can be used for receiving the released ions indefinitely. Ifnecessary, the restored CDI module may be rinsed with a pure liquidbefore being placed back for the next run of deionization. Afterrinsing, the waste liquid may be added to the reservoir of liquid 24 asa regeneration medium. Though only two compartments and two electrodemodules are shown in FIG. 1A, other numbers of compartments and CDImodules can be used to meet application needs. Using recurrentdeionization and energy extraction, the present invention can thusco-generate purified liquids and electricity.

As shown in FIG. 1A, the modules comprise 7 pairs of stacking electrodesconnected in parallel. There is an insulating spacer in the form ofscreen, mesh, net, network, web or comb (not shown) interposed betweenevery two electrodes to prevent electrical short. To serve its purpose,the spacer should be inert, non-adsorptive, and non-leachable. Materialssuch as PE (polyethylene), PP (polypropylene), PVC, Teflon and Nylon maysatisfy the foregoing requirements. Preferably, the spacer should have awidth smaller than 0.2 mm, preferably from 0.05 mm to 0.1 mm, to allowfree pass of liquids. Activated carbon made from precursors such ascoconut shell, pitch, coal, polyurethane, and polyacrylonitrile (PAN)can be employed as the electrosorption medium. Moreover, carbon nanotube(CNT) with appropriate tube diameters, for example, from 2 nm to 50 nm,is an ideal material for preparing the CDI electrodes. Mixed with afluorinated binder and a solvent, powder of activated carbon or CNT isconverted to a homogeneous paste suitable for roller coating onsubstrates. Titanium foil of 0.05 mm or less is used as the substratefor anodes, while copper foil of 0.02 mm or less for preparing thecathodes. Suitable metal leads are attached to the electrodes by spotwelding or soldering. Electrodes are then stacked with a screen spacerdisposed between every two electrodes. Using an insulating tape, or twoplastic plates and at least two bolts and two nuts (not shown in FIG.1A), the whole stack of electrode and spacers are secured to form a CDImodule. Assembled without encapsulation as aforementioned, the modulemay be submerged in liquids to be treated for deionization. In addition,if the electrodes and spacers can be spirally wound into an open roll,it can be installed in conduits for deionizing liquids that flow freelythrough the electrodes. The CDI electrodes may be connected in parallelfor higher surface area, or in series for higher applied voltage, or inhybrid mode for a special need.

FIG. 1B is another top view of the deionizer with energy recovery. B isa DC power source that includes rectified AC power, batteries, solarcells, and fuel cells. Only a DC voltage of 1˜3V is required to sustainelectrosorption of the CDI module in compartment 12 of carousel 10.However, a higher voltage may be used to provide both electrosorptionand electrolysis with benefits more than just deionization. As disclosedin U.S. Pat. No. 6,328,875 issued to Zappi et al, which is incorporatedherein as reference, disinfection of microorganisms and organicpollutant was realized by using electrolysis. Occasionally, electrolysismay be utilized to generate oxidants to prevent fouling of the CDIelectrodes. Nevertheless, the present invention is primarily designedfor deionization, and electrolysis is generally avoided. Block 26 is amicroprocessor that performs three functions: (1) to monitor thepotential developed across the electrodes of CDI modules; (2) toactivate and deactivate the motor of carousel; and (3) to regulateenergy extraction. Load C can extract the residual energy from the CDImodule in compartment 14, whereby the CDI module is restored at the sametime, through anode 16′ and cathode 18′. It is preferably to store thereclaimed energy in devices such as supercapacitors, ultracapacitors, orelectric double layer capacitors. Because all of the foregoingcapacitors are cable of accepting any magnitude of current withoutmechanical movement, they have better charging efficiency than batteriesand flywheel. Moreover, the capacitors can be fabricated more compactthan flywheel. As the potential developed across the electrodes ofcapacitors equals the source voltage, energy transfer will be ceased. Atthis point, the CDI module may not be completely regenerated for someresidual energy is still present on the electrodes. One way to solve theproblem is by using a power bank consisting of many capacitors, or anelectronic energy-extractor. In order to minimize loss at energyextraction, the internal resistance or ESR (equivalent seriesresistance) of the supercapacitors should be as low as possible.

FIG. 2A is a side view of yet another preferred embodiment of arranginga deionizer with energy recovery in Ferris wheel configuration. For thepurpose of simplification, only two compartments 205 and 207, as well astwo CDI electrode modules 213 and 215 are shown in container 201. Otheraccessories including power source, microprocessor and load are omittedfor they are similar to those in FIG. 1B. Ferris wheel 200 has motorsbuilt inside the central pole 213 to provide lifting motion for thelever 203 with electrode modules 213 and 215 from position A to positionB, and to switch the CDI modules from deionization to regeneration orvice versa. Nevertheless, the distance between A and B is not drawn toreflect the real size that allows enough clearance for the CDI modulesto be rotated. Compartment 205 is designated for regeneration wherein apure liquid or the same solution as liquid to be treated in compartment207 is used indefinitely as regeneration medium. Compartment 207 isdesignated for deionization wherein contaminated liquids or seawater canenter the compartment by inlet 209 and exit the compartment from outlet211 once they are purified. Due to two simple movements are demanded,motors of Ferris wheel 200 should consume little amount of energy andthey may be operated by the same power source that sustainsdeionization.

FIG. 2B shows a Ferris wheel 400 containing 8 compartments with 8 CDImodules represented by 408. On each module, there is a control modulerepresented by 402 containing a microprocessor and a step-up circuitryfor draining the residual energy of the CDI module. Each module ismounted to a lever represented by 203 where a control module is disposedon the top of the CDI module. The control module can monitordeionization, activate and deactivate mechanical movements, as well asregulate energy extraction. There are motors built inside the centralpole 217. The compartments are divided into 4 sections where 404 is fordeionization, 406 for regeneration, areas A and B are waiting quartersfor the CDI modules to be treated for minimizing cross contamination.

FIG. 3 is still another preferred embodiment wherein a moving belt 37,which is engaged by rollers represented by 38, carrying a number of CDImodules represented by 33 in cylindrical form for recurrent deionizationand regeneration. Both liquids to be treated 31 and regeneration medium35 can flow freely through the CDI electrodes. After deionization,fluent 32 may become a purified liquid, while fluent 36 will be enrichedby the ions discharged at regeneration. As in FIG. 2B, each CDI moduleis equipped with a control module represented by 34. Area labeled 40 isthe waiting quarter where the CDI modules are post-treated to reducecross contamination.

FIG. 4 is the diagram of the foregoing control module that is composedof a step-up circuitry S, a microprocessor PWM and a supercapacitor L.In FIG. 4, B is a DC power source to provide electricity to CDI fordeionization. Then, the residual energy of CDI can be discharged via Sto supercapacitor L. Normally, S is off until the potential of CDI isequal or smaller than the voltage of L. When the latter situationoccurs, microprocessor PWM will raise the potential of CDI through S toabove the voltage of L to completely drain the residual energy of CDI.Using an electronic energy extractor as PWM and S, electrodes of CDI canbe quickly restored. The microprocessor PWM also activates anddeactivates motor M so that the CDI modules can be switched to thedesired positions.

Instead of using an automatic carousel or Ferris wheels setup, the CDImodules in the following examples are switched between deionization andregeneration manually. Experimental are presented to demonstrate thatthe CDI modules can 1) directly purify seawater or waste liquids withhigher salt content; 2) undergo numerous cycles of sorption anddesorption without degradation; and 3) convert the power density of apower source.

EXAMPLE 1

A CDI module is composed of 4 cells connected in series wherein eachcell consists of 2 parallel electrodes with a PVC screen disposed in themiddle. Each electrode has a dimension of 6 cm×5 cm×0.35 mm and uses oneactivated carbon (surface area 1050 m²/g at $0.30 per pound) as theelectrosorptive medium. The module is placed in seawaters of differentsalt content, namely, 5,000 ppm, 20,000 ppm and 35,000 ppm (original)for potentiostatic deionization using 8 DC volt. As the potentialdeveloped across the cells reaches 8V and current has declined to asteady value, the deionization is terminated. Then, the residual energyof the module after deionization performed on each solution isdischarged to an electronic load. Recovery efficiency of each energyextraction is calculated and listed in Table 1:

TABLE 1 Recovery Efficiency of the Residual Energy after CDI EnergyInput Energy Recovered Efficiency Seawater (ppm) (Joule) (Joule) (%)20,000 3.42 0.22 6.5 35,000 5.27 0.98 18.5

Energy transfer in the 5,000 ppm seawater is too little to be measured.It appears that the recovery efficiency is higher with higher saltcontent.

EXAMPLE 2

The same CDI module as Example 1 is fully charged in 35,000 ppm seawateras Example 1. Afterwards, the residual energy is used to charge twocommercial supercapacitors, and Table 2 shows the charged status thecapacitors,

TABLE 2 Residual Energy of CDI Stored in Supercapacitors SupercapacitorVoltage Developed Peak Current Specification (V) Delivered (A) 2.5 V ×20 F  1.9 4.1 2.5 V × 100 F 0.45 9.5

As shown in Table 2, the residual energy after CDI can be saved forpractical applications, and supercapacitors are well suited for theapplications.

EXAMPLE 3

The same CDI module as Example 1 is fully charged in 35,000 ppm seawaterusing a constant current of 5A. Immediately after the termination ofcharge, the module is discharged to an electronic load where a peakcurrent of 39A is measured. Therefore, the CDI module behaves as a powerconverter for the peak current is much higher than the charge current.

EXAMPLE 4

A new CDI module is prepared by connecting 32 pieces electrodes of 6cm×5 cm×0.35 mm in parallel to form one anode and one cathode. Theelectrodes use the same activated carbon as Example 1 as theelectrosorptive medium. The module is used for directly removing ions ofa waste liquid with a salt content of 122,000 ppm from a dye factory. Ineach cycle of process, the module is applied 3 DC volt for 5 minutes fordeionization, then the module is discharged quantitatively to anelectronic load with the module immersed in a regeneration medium, whichis DI water, in a separate container. Only the first six consecutivecycles of deionization and regeneration is shown in Table 3.

TABLE 3 Purification of a 122,000 ppm Waste Liquid by RecurrentDeionization and Regeneration Original Liquid Regeneration Liquid #(ppm) Δ ppm (ppm) Δ ppm 1 116,500 5,500  7,000 — 2 110,000 6,000 14,2006,500 3 105,000 5,000 21,100 6,900 4 101,000 4,500 27,750 6,650 5 95,500 5,500 33,000 5,250 6  89,500 6,000 38,000 5,000

Theoretically, column 3 and column 5 of Table 3 should contain the samenumbers the discrepancy may be due to cross contamination and/ormeasurement errors. Nevertheless, Table 3 clearly demonstrates that theCDI module in conjunction with the recurrent deionization andregeneration can directly and continuously purify liquids with extremelyhigh salt content. Furthermore, the amount of ions removed in each cycleis significant indicating that the present invention is a very usefulseparation technique.

On the other hand, when the deionizer of this invention is used as apower converter, the electrolyte used in the power converter may containcations selected from the group consisting of H⁺, NH₄ ⁺, alkali metal,alkali earth metals, transition metals, and the combinations thereof.The electrolyte may contain anions selected from the group consisting ofOH⁻, halides, NO₃ ⁻, ClO₄ ⁻, SO₃ ²⁻, SO₄ ²⁻, PO₄ ³⁻, and thecombinations thereof. In addition, the electrolyte may use a solventselected from the group consisting of water, methanol, ethanol, acetone,acetonitrile, propylene glycol, propylene carbonate, ethylene carbonate,and the combinations thereof. A protection case is also required tohermetically seal the electrode module in the power converter.

The above description in conjunction with various embodiments ispresented only for illustration purpose. There are many alternatives,modifications and variations that are apparent to persons skilled in theart in light of foregoing detailed description. It is intended toinclude all such alternatives in the spirit and scope of the appendedclaims.

What is claimed is:
 1. A power converter, comprising: an electrodemodule containing an anode, a cathode and at least one ionicallyconductive spacer interposed between the anode and the cathode toprevent electrical short and to maintain ion transfer between theelectrodes; an electrolyte in liquid for providing anions and cationsfor reversible adsorption and desorption on the electrodes; and aprotection case for hermetically sealing the electrode module.
 2. Thepower converter of claim 1, wherein the electrode module containing aplurality of electrodes that are stacked and connected in parallel or inseries to form the anode and the cathode, while the ionically conductivespacer is interposed between every two electrodes.
 3. The powerconverter of claim 1, wherein the anode, the cathode and two ionicallyconductive spacers spirally wound into a roll.
 4. The power converter ofclaim 1, wherein the electrolyte has a salt content of 5,000 ppm orhigher.
 5. The power converter of claim 1, wherein the electrolytecontains cations selected from the group consisting of H⁺, NH₄ ⁺, alkalimetal, alkali earth metals, transition metals, and combinations thereof.6. The power converter of claim 1, wherein the electrolyte[conains]includes anions selected from the group consisting of OH⁻,halides, NO₃ ⁻, ClO₄ ⁻, SO₃ ²⁻, SO₄ ²⁻, PO₄ ³⁻, and combinationsthereof.
 7. The power converter of claim 1, wherein the electrolyte usesa solvent selected from the group consisting of water, methanol,ethanol, acetone, acetonitrile, propylene glycol, propylene carbonate,ethylene carbonate, and combinations thereof.